PNNL

Abstract

The Department of Energy’s (DOE’s) National Energy Technology Laboratory’s (NETL’s) Blowout and Spill Occurrence Model (BLOSOM), and the National Oceanic and Atmospheric Administration’s (NOAA’s) General NOAA Operational Modeling Environment (GNOME) are compared. Progressively more complex simulations are used to assess similarities and differences between components of the two models. The comprehensive comparison between GNOME and BLOSOM presented here, should aid modelers in interpreting their results when using both models, and should aid modelers understand their results even when using only one of them. Beyond many similarities, the comparison also highlights aspects where both models could improve, e.g. the inclusion of temporal interpolation of the forcing fields (BLOSOM) or the inclusion of a deflection angle option (GNOME). Overall, GNOME and BLOSOM perform similarly, and are found to be complementary oil-spill models. The increasingly-complex approach used in our comparison tests is also used, in parallel, to illustrate, the approach an oil-spill modeler would typically pursue to understand the main drivers behind an oil spill. Additionally, some of these tests are also used to investigate the drivers of the Point Wells spill which occurred on December 30, 2003 in the Salish Sea. The simulations presented here are forced by ocean currents simulated with a finite volume community ocean model (FVCOM) that have excellent skill in representing tidal motion, and with observed wind data, that compensates for a coarse vertical ocean-model resolution. The oil-spill models’ solutions are compared to the historical Point Wells’ oil trajectory, in time and space, as determined from overflight information. Our hindcast of the Point Wells spill is successful in broadly replicating the correct locations at the correct times of the observed trajectory using accurate tide and wind forcing. While the choice of wind coefficient we use is unconventional, we use an analytic model supported by observations, to conclude that under the circumstances of this study, it well may be justified. Beyond the models’ comparison, we present additional results and relevant information. We discuss our successful hindcast of the Point Wells oil spill that, to our knowledge, had remained unexplained for over a decade, including recommendations for future studies. We highlight some of the key oceanographic findings as they may relate to other oil spills, and to the regional oceanography of the Salish Sea. Finally, within the flow of the tests with which we compare GNOME and BLOSOM, we have highlighted the processes an oil-spill modeler would typically follow when trying to hindcast or forecast an oil spill, including detailed technical information on basic aspects like choosing a computational time step. Thus, beyond comparing two oil-spill models, this paper sheds light on what drove the historical Point Wells spill, and serves the additional purpose of being a learning resource for those interested in pursuing oil spill modeling.